Wireless telephones, such as cellular phones, have become popular beyond expectation. Cellular phones are supported by cellular telephone systems which typically include a mobile telephone central switching exchange being connected to a multitude of geographically distributed cellular radio stations via a corresponding multitude of multichannel trunks. In populous areas, cellular systems are rapidly becoming overloaded with the result that mobile telephone services are sometimes degraded or simply unavailable. As an alternative to the cellular systems, a new standard referred to as CT2 has been recommended. This standard defines low power radio links, in a different portion of the radio frequency spectrum with respect to that of the cellular spectrum, and being functional over much shorter distances, for example distances of up to about 200 metres. It has been realized that the typical cellular system structure and radio link control methods are inefficient and unsuitable for direct application in a telephone switch incorporating the CT2 standard.
It is an object of the invention to provide a low power wireless telephony service, being supported by a small telephone system.
Small telephone systems are of two different basic architectures, namely that of a key telephone system, and that of a telephone branch exchange. In these systems, individual associated telephone sets have traditionally been wire linked to the system.
The branch exchange includes a call controller which is commonly accessible to all the telephones connected to the branch exchange. Telephone operations and telephony features are centrally provided. Beyond some minimum size, the branch exchange is more economical than the key telephone system. A wireless system supported by a branch exchange is disclosed in U.S. Pat. No. 4,771,448.
Key telephone systems are characterised in that there is little or no apparatus which is commonly accessible to the telephones connected to the system. The primary advantage of key telephone systems is one of economy with small size.
Examples of small telephone systems, are disclosed in each of U.S. Pat. Nos. 4,873,682, 4,893,310 and 5,136,585 issued in the names of George Irwin et al, David Robertson et al, and Nadir Nizamuddin et al respectively, each being titled "Digital Key Telephone System". A small telephone system is discussed by Brian Jervis et al in an article titled "New generation in key system design", pages 5-20; and is discussed by David Lynch et al in an article titled "System Architecture", pages 21-29, both published by Bell-Northern Research in Telesis 1989, Number 2. These publications are exemplary of the form of some telephone systems wherein the invention may be embodied.